The invention relates to the field of power electronics. It relates specifically to a cooling device for a high-power semiconductor module as claimed in the preamble claim 1, and to a method for producing such a cooling device, as claimed in the preamble of patent claim 7.
High-power semiconductor modules, such as those that are known from EP-A-0,597,144, have a number of semiconductor components (for example thyristors, IGBTs or diodes) which are combined in a common housing to form a logical functional unit. Such high-power semiconductor modules are nowadays operated in a voltage range up to 6.5 kV, and require appropriate cooling. To this end, the semiconductor components are soldered on a common cooling device, through which a cooling liquid generally flows. Heat sinks composed of aluminum are generally used as the cooling devices. However, aluminum has the disadvantage that its thermal coefficient of expansion is not matched to the corresponding coefficients of the semiconductor components, in particular to their electrical insulation plates or to the semiconductor chips. In consequence, mechanical stresses occur which lead to fatigue in the solder layers between the semiconductor components and the cooling device, and thus to the electrical contacts becoming detached.
DE-A-196,43,717 therefore proposes a cooling device whose thermal coefficient of expansion is matched to that of the semiconductor components. A cooling device is used for this purpose which is produced from a metal matrix composite, in particular from aluminum silicon-carbide (AlSiC) or copper silicon carbide (CuSiC). The production of such a metal ceramic composite material is described, for example, in James A. Cornie, Advanced Pressure Infiltration Casting Technology Produces Near-absolute Net-Shape Metal Matrix Composite Components Cost Competitively, Materials Technology, Vol. 10, No. 34, March/April, 1995.
This cooling device preferably has cooling elements in the form of studs or ribs, in order to increase the cooling area and thus to improve the heat transfer, so that it has a relatively complex geometry. In a first embodiment, the cooling device is cast integrally from the metal matrix composite. However, cooling devices such as this are relatively expensive, since, particularly if they have complex geometries, their production is expensive and, furthermore, they are composed of relatively expensive material. In another embodiment, only a cooling plate is composed of the metal matrix composite and the remainder is manufactured from a low-cost material, in particular from plastic, with the two parts being bonded together. A disadvantage of this embodiment is that the bonded joint is subject to age-dependent fatigue phenomena.
A further cooling device is known from EP-A-0,661,917. This cooling device comprises a cooler lower part and a cooler upper part, with the cooler lower part being connected to the cooler upper part by an integral material connection. Both cooler parts are composed of a metal matrix composite (MMC), for example aluminum silicon-carbide. The integral material connection between the cooler parts is produced during the production process. For this purpose, ceramic preforms of the cooler parts are produced first of all, these are then placed one on top of the other, and metal is then infiltrated into both parts. The joint infiltration is intended to allow the metal to flow through the pores of both parts by capillary action, and thus to connect them together. Owing to the complexity of their production and owing to the choice of the material, these cooling devices are also relatively expensive. Since the quality of the connection depends on the capillary action, it is, furthermore, difficult to produce a sufficiently dense composite, depending on the shape of the cooler parts.
It is therefore an object of the invention to provide a cooling device of the type mentioned initially, which can be produced at low cost and easily.
This object is achieved by a cooling device having the features of claim 1, and by a method for producing a cooling device having the features of claim 7.
The cooling device according to the invention comprises a cooler lower part and a cooler upper part, with the cooler upper part having a cooling plate composed of a metal matrix composite, preferably aluminum-silicon carbide, on which a metal border is integrally formed. The two cooler parts are in this case connected to one another via the metal border by an integral material connection.
The cooling plate and the metal border can be manufactured in the same production step by using excess metal to form the metal border during metal infiltration of a ceramic preform in order to form the cooling plate.
The metal border which is integrally formed on the cooling plate allows a strong and long-lasting connection to be produced in a simple way between the cooler upper part and the cooler lower part. The cooler lower part can be produced from low-cost material which is easy to form and process, in particular from aluminum. Suitable choice of the material for the cooler lower part allows stresses and faults in the connection to be avoided. The cooler lower part is preferably manufactured from the same material as the cooler upper part. Friction welding is preferred as the connection method, since this leads only to a local influence from heat in the cooling device.
Such a cooling device combines the advantages of the already known cooling elements composed of metal matrix composite with the advantages of the already known aluminum cooler and can be produced simply and at low cost. The special border allows it to be connected to the cooler lower part in a simple manner, and faults can be avoided.
Further advantageous embodiments are evident from the dependent patent claims.